Why are the genes involved in lactose metabolism considered to be an operon?

The genes involved in metabolism of lactose are considered an operon because the same promoter regulated all of them.

Explanation:

The genes involved in metabolism of lactose are considered an operon because the same promoter regulated all of them. The promoter is the coordinating site for the encoding of RNA polymerase, the enzyme.

The lac operon is a single promoter operon, or band of genes. The operon genes encoded proteins that enable lactose to be used as a source of energy by the bacteria.

An operon consists of a number of structural genes which are transcribed together under a single promoter. Hence these genes are expressed together. There is also an operator between the promoter and the structural genes which controls the transcription process.

Three genes involved in lactose metabolism have the same promoter and operator. These genes are lacZ, lacY and lac A. lacZ encodes for an enzyme that cleaves lactose into galactose and glucose. lacY is responsible for pumping of lactose inside the cells and lacZ and lacA codes for an enzyme that shifts an acetyl group from acetyl-CoA to β-galactosides. All these genes are involved in lactose metabolism and are transcribed simultaneously hence they form part of an operon.

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